In recent years, rapid improvement of ink-jet recording materials has been realized, resulting in almost similar quality to that of conventional silver halide photography. Specifically, in order to achieve image quality comparable with silver halide photography by ink-jet recording, improvement has been enhanced in regard to ink-jet recording sheets. Porous type recording sheets comprise a very flat and smooth support having a porous layer of minute voids thereon, which comprises a pigment and a hydrophilic polymer, exhibits high glossiness and brilliant coloration, and further exhibits superiority in ink absorbability and drying, resulting in a material showing almost identical quality of silver halide photography. Specifically, when a non-absorbing support is employed, a much higher quality print can be obtained, since cockling after printing, so-called wrinkling, is not generated, which is often observed on an absorbing support, resulting in maintaining excellent smoothness of the surface.
Ink-jet recording is generally divided into two categories, one of which is using a water based ink employing water and a water soluble solvent as ink solvents, and the other is using a non-water based ink employing an oil soluble solvent. Each of these consists of two types, using either a dye or a pigment as a colorant, and thus, it is necessary to use specially prepared sheet adaptive to each type to obtain the desired high quality recorded images. As to ink, water based ink is the more common type due to a lesser burden on the environment, and handling safety.
Pigment ink results in high durability of images, but tends to change glossiness of the image as imagewise, resulting in lowered image quality. On the other hand, when water soluble dye ink is used, color prints with sharp image details and also uniform surface glossiness can be obtained, the quality of prints is comparable with silver halide photographic quality.
However, even though this water soluble dye can form high quality images, its image stability is inferior to that of pigment ink images. Therefore, relatively severe discoloration by sunlight or indoor light, or by an oxidizing gas such as ozone in ambient air has been a major issue. Specifically, in a porous type recording sheet provided a porous layer of minute voids thereon, the contact area of a dye and ambient air is large, the result is that the dye images tend to be easily affected by oxidizing gases in ambient air. Thus, it has remained a desire to overcome these problems.
To prevent these problems of deterioration with storage, numerous addition of various anti-oxidizing agents as anti-discoloration agents (or light-fastness improving agents) have been proposed.
Examples of these proposals include, for example, ink-jet recording sheets containing various compounds as anti-oxidizing agents as described in JP-A Nos. 57-87989, 57-74192 and 60-72785 (hereinafter, the term JP-A refers to as Japanese Patent Application Publication); ink-jet recording sheets containing ultraviolet absorption agents as described in JP-A 57-74193; addition of hydrazides as described in JP-A 61-154989; addition of hindered amine type anti-oxidizing agents as described in JP-A 61-146591; addition of nitrogen-containing heterocyclic mercapto compounds as described in JP-A 61-177279; addition of thioether type anti-oxidizing agents as described in JP-A Nos. 1-115677 and 1-35479; addition of specific structured hindered phenol type anti-oxidizing agents as described in JP-A 1-36480; addition of hindered phenol type anti-oxidizing agents in combination with hindered amine type anti-oxidizing agents as described in JP-A 3-13376; addition of ascorbic acides as described in JP-A Nos. 7-195824 and 8-150773; addition of zinc sulfate as described in JP-A 7-149037; thiocyanates to be incorporated as described in JP-A 7-314882; addition of thiourea derivatives as described in JP-A 7-314883; saccharides to be incorporated as described in JP-A Nos. 7-276790 and 8-108617; addition of phosphoric acid type anti-oxidizing agents as described in JP-A 8-118791; addition of nitrites, sulfites or thiosulfates as described in JP-A 8-300807; and addition of hydroxylamine derivatives as described in JP-A 9-267544.
However, in an ink-jet recording sheet having minute pores, the desired effects of the addition of an anti-oxidizing agent is not always adequate. In cases when these various anti-discoloration agents are added in a large amount, the problem of lowered ink absorbability of a porous layer exists.
On the other hand, it is well known that resins having unsaturated bonds in a molecule, such as butadiene rubber, can be employed in ink-jet recording sheets. For example, using methods for the resins to mainly absorb solvents of oil based ink are disclosed in JP-A Nos. 2000-177234, 2000-238407, 2001-205929, 11-165460, 11-99742 and WO 00/41890. Further, a method to improve absorbability of water based ink is disclosed, in which a diene type polymer or its hydrate is sulfonated to become hydrophilic. Still further, it is also disclosed that storage stability is improved by combination with a specific dye using styrene-butadiene latex containing 20–45% of a butadiene component as a binding agent, in which the latex is used as a binding agent, resulting in a low butadiene ratio, and therefore, resulting in a limited effect. Furthermore, the technology to prevent bleeding over time under high temperature and high humidity and to prevent discoloration of formed images over time, by adding a compound having an aliphatic carbon-carbon double bond in the molecule (for example, patent documents 1 and 2), but its anti-gas discoloration effect is insufficient.
Patent document 1: JP-A 2002-264478
Patent document 2: JP-A 2000-263928